know how to dismantle it & fix it? The Landcruiser is an 80 series, made in 1995. It is a manual petrol model.
Any help or directions to help at all would be greatly appreciated.

Take it to the Toyota dealership.

If it is the whole assembly, the inside of door should have a small plastic piece that either snaps or screws on. Remove to find three to four small nuts holding mirror. If it is just the reflective mirror i recommend replacing the whole assembly. (try a good junk yard)

I've ran into this problem before. any time I've had a vehicle with a broken mirror and replaced it with an aftermarket (made in china) version. they all vibrate. best you can do is make sure everything is tight. good luck